1. Field of the Invention
The present invention relates to a method for melting a rod material such as magnesium and aluminum in a material melting and holding apparatus of a metal molding apparatus.
2. Description of the Prior Art
As an injection apparatus for metal molding, Japanese Laid-Open Patent Publication No. 2004-291032 discloses an apparatus having such a structure that a melting furnace is provided on an injection cylinder internally containing a plunger, a solid material is melted by the melting furnace, the molten material is reserved in the melting furnace, the molten material in the melting furnace is sucked and accumulated in a material measurement chamber in front of the plunger formed by a backward travel of the plunger for measurement of the molten material in a quantity of one shot, and the measured material is injected from a nozzle at a tip of the cylinder into a mold by a forward travel of the plunger.
Moreover, as an injection apparatus for metal molding using a material rod as a material for molding, Japanese Laid-Open Patent Publication No. 2005-40807 discloses an apparatus having such a structure that a heat holding reserve cylinder is erected in a solution retaining chamber of an injecting and heating cylinder internally containing an injection plunger, a melting apparatus provided with a heating cylinder extending in the widthwise direction is provided on the top side of the heat retaining reserve cylinder, material rods are melted by the heating cylinder, the molten material is held in a quantity corresponding to multiple shots in the heat retaining reserve cylinder, the molten material in the solution retaining chamber is sucked and accumulated in a material measurement chamber in front of the injection plunger formed by a backward travel of the plunger for measurement of the molten material in a quantity of one shot, and the measured material is injected from a nozzle at a tip of the cylinder into a mold by a forward travel of the plunger.
Moreover, Japanese Laid-Open Patent Publication No. 2006-809 discloses an apparatus having such a structure that a melting cylinder for rod materials is erected on heating and holding cylinder internally containing an injection plunger, the material rods are melted by the melting cylinder, the molten material is reserved in a quantity corresponding to multiple shots in the heating and holding cylinder, the molten material in the heating and holding cylinder is sucked and accumulated in a material measurement chamber in front of the injection plunger formed by a backward travel of the plunger for measurement of the molten material, and the measured material is injected from a nozzle at a tip of the cylinder into a mold by a forward travel of the plunger.
In the conventional apparatus which melts the solid material in the melting furnace, reserves the molten material, measures the molten material in a quantity of one shot for each backward travel of the plunger, and injects the measured material, the solid material supplied is submerged and melted by the molten material which has already melted in the melting furnace. Thus, if a molten material is present in the melting furnace, even a material rod is melted in a short period. However, if no molten material is present in the melting furnace upon startup of molding, the material rods supplied into a furnace body are melted by radiant heat from a periphery and a bottom portion of the furnace body, which is less efficient in heating than the submersion melting, and it takes a long period until multiple material rods are melted, and the molten material thus reaches a reserved quantity sufficient for submersing and melting the material rods. As a result, if the rod materials are melted by the melting furnace, the startup of the molding takes as long as 60 minutes, and there poses a problem of inefficient molding operation.
Moreover, when the material is melted by the melting furnace, the temperature of the supplied material is lower than the molten material, so the temperature of the molten material around the solid material decreases each time the material is supplied, thus, in order to prevent this temperature fluctuation from affecting the molten material supplied to the injection cylinder, the material rods are heated in advance at other location thereby decreasing the difference in temperature from the molten material, and then bringing and supplying the material to and into the melting furnace, which is inconvenient.
In the melting method of storing and melting material rods in the melting cylinder, though the material is melted by the radiant heat, which is less efficient in melting than the submersion melting, the entire material receives the ambient radiant heat, the heating efficiency is significantly high, the melting can be maintained by simply inserting material rods into the melting cylinder, the molten material can be reserved and held in a heat retaining reserve cylinder of a injecting and heating cylinder or a heating and holding cylinder, so the molding startup period can be approximately 20 minutes, and the molding operation can start earlier than a case in which the material rods are melted directly by the melting furnace. Moreover, this method has an advantage that the temperature drop due to the material supply does not happen in the melting furnace. However, the quantity of the material reserved after melting is restricted, melting and supplying a material adapted to a molding cycle may thus be difficult depending on the weight of a metal product, and this method has a problem that it is hardly applicable to a large machine.